Field of the Invention
This invention relates to a plumb device for the determination of vertical and horizontal directions, in which a direction determination unit with a luminous source is suspended from a universal joint so that it is freely usable, so that after levelling out in the equilibrium state, a directional light beam from the luminous source indicates the vertical direction.
A plumb device having such characteristics is disclosed, for example, in the German Unexamined Patent Application 25 49 218. To determine directions, it has a suspended, freely-moving image generator, whose optical axis is oriented vertically during the levelling out. The universal joint itself consists of two joint parts, one of which is rigidly connected to the stand housing, while the other can move with the direction determination unit relative to it.
German Unexamined Patent Application 26 34 456 also discloses a ball and socket joint for the vertical orientation of a plumb bob. But the plumb bob can also be suspended by a cardan joint, as disclosed in British Patent Specification 1 375 710, so that it swings freely on a line. However, such suspensions all have certain disadvantages.
The ball and socket joint disclosed in the German Unexamined Patent Application 26 34 456 is not suitable for precision plumb bobs, on account of its internal joint friction, since with small plumb devices in particular, there are only small return forces available for the orientation. Moreover, the joint parts of the suspension must be manufactured with precision, since any imprecision reduces the accurate vertical orientation of the measuring unit. The universal joint disclosed in German Unexamined Patent Application 25 49 218 also has such disadvantages, and even cardan joint suspensions, like those used for example to hold a ship's compass horizontal, are not sufficiently accurate.
An additional advantage of the above-mentioned plumb bobs is that external vibrations--e.g. from a running machine--can be transmitted to the freely suspended masses. The levelling out of the plumb bob can therefore take a very long time. German Unexamined Patent application 25 49 218 discloses an oil damping mechanism to solve this problem, but it reduces the sensitivity.